/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.nineoldandroids.animation;

/**
 * This evaluator can be used to perform type interpolation between integer
 * values that represent ARGB colors.
 */
@SuppressWarnings("rawtypes")
public class ArgbEvaluator implements TypeEvaluator {

	/**
	 * This function returns the calculated in-between value for a color given
	 * integers that represent the start and end values in the four bytes of the
	 * 32-bit int. Each channel is separately linearly interpolated and the
	 * resulting calculated values are recombined into the return value.
	 * 
	 * @param fraction
	 *            The fraction from the starting to the ending values
	 * @param startValue
	 *            A 32-bit int value representing colors in the separate bytes
	 *            of the parameter
	 * @param endValue
	 *            A 32-bit int value representing colors in the separate bytes
	 *            of the parameter
	 * @return A value that is calculated to be the linearly interpolated
	 *         result, derived by separating the start and end values into
	 *         separate color channels and interpolating each one separately,
	 *         recombining the resulting values in the same way.
	 */
	public Object evaluate(float fraction, Object startValue, Object endValue) {
		int startInt = (Integer) startValue;
		int startA = (startInt >> 24);
		int startR = (startInt >> 16) & 0xff;
		int startG = (startInt >> 8) & 0xff;
		int startB = startInt & 0xff;

		int endInt = (Integer) endValue;
		int endA = (endInt >> 24);
		int endR = (endInt >> 16) & 0xff;
		int endG = (endInt >> 8) & 0xff;
		int endB = endInt & 0xff;

		return (int) ((startA + (int) (fraction * (endA - startA))) << 24)
				| (int) ((startR + (int) (fraction * (endR - startR))) << 16)
				| (int) ((startG + (int) (fraction * (endG - startG))) << 8)
				| (int) ((startB + (int) (fraction * (endB - startB))));
	}
}